“Sodium and water” experiment
Pieces of sodium rapidly run on water
Can we make metal run across water? Let’s find out!
Only work in protective gloves, glasses and a mask. Observe safety rules when working with flame and flammable objects, and when working with active metals such as lithium, sodium, potassium, rubidium and cesium.
Reagents and equipment:
- metallic sodium;
- 1% sol. phenolphthalein4
- 1% sol. indigo carmine;
- 1% sol. thymol blue;
- glass bowls
Pour water into the glass bowls, then add the indicator solutions – phenolphthalein to the first, indigo carmine to the second and thymol blue to the third. Add a piece of metallic sodium. Watch the change of color in all three bowls.
If you throw a small piece of sodium into a bowl of water containing an acid base indicator, you’ll see an impressive effect: the sodium starts to speed across the surface, and it also dissolves, forming a bead which can even ignite, turning into a fiery ball!
Why does sodium run
When it reacts with water, hydrogen is released, which makes the sodium start “running”.
Why does sodium dissolve and ignite
The reaction of sodium with water takes place with an enormous release of heat, which is sufficient to melt metal and turn it into a bead, which is actually a ball of dissolved metal. Additionally, the energy of this reaction is sufficient to ignite the hydrogen released!
Why does the color in the bowls change
Phenolphthalein, indigo carmine and thymol blue are acid base indicators, i.e. substances that change their color when the hydrogen index of the medium changes. When sodium reacts with water, sodium hydroxide is formed, which is a very strong base, and the medium becomes alkaline. Indicators change their color in the following way: phenolphthalein from colorless to crimson, indigo carmine from blue to green, and thymol blue from yellow to blue:
2Na + 2H₂O = 2NaOH + H₂